Clinically significant hyperargininemia results from mutations in the Type I arginase gene (Arginase I) (Cederbaum S D, et al., 1979, Pediat Res 13:827-833;
Cederbaum S., et al., 1977, J. Pediatr 90:569-573; Michel V V, et al., 1978, Clin Genet 13:61-67) which is predominantly expressed in the liver and red blood cells (Gasiorowska I, et al., 1970, Biochim Biophys Acta 17:19-30; Hermann B G and Frischauf A-M., 1987, Meth Enzymol 152:180-183; Spector E B, et al., 1982, Biochem Med 28:165-175.) Arginase I deficient patients present with spasticity, growth retardation, progressive mental impairment and episodic hyperammonemia (Cederbaum S D, et al., 1979, Pediat Res 13:827-833; Cederbaum S D, et al., 1977, J. Pediatr 90:569-573; Thomas K R and Capecchi M R, 1987, Cell 51:503-512.) Although significantly devastating, Arginase I deficiency has a milder clinical phenotype than other urea cycle disorders. It has been proposed that the presence of a second isoform of arginase might be responsible for this milder presentation (Grody W W., et al., 1989, J Clin Invest 83:602-609; Grody W W, et al., 1993, Hum Genet 91:1-5) The existence of an extra-urea cycle form of arginase (Arginase II), which localizes to the mitochondria (Wissmann P B, et al., 1994, Am J Hum Genet 55:A139), has been demonstrated utilizing various non-cross reacting antibodies to Arginase I and Arginase II (Spector E B, et al., 1983, Pediatr Res 17:941-944). In patients deficient in type I arginase activity, a compensatory up regulation of Arginase II has been observed (Gasiorowska I, et al., 1970, Biochim Biophys Acta 17:19-30; Hermann B G, et al., 1987, Meth Enzymol 152:180-183). Using these antibodies, it has been established that Arginase II is expressed predominantly in the kidney, but is also found in the brain, activated macrophage, the gastrointestinal tract and in the lactating mammary gland (Spector E B, et al., 1983, Pediatr Res 17:941-944.) Arginase II is not expressed at a significant level in the liver or red blood cells. In addition to a hypothetical role in the production of proline and glutamate it has been postulated that Arginase II may play an important role in nitric oxide biosynthesis through the production of ornithine as a precursor of glutamate (Mezl V A, et al., 1977, Biochem J 164:105-113; Wang W W, et al., 1995, Biochem Biophys Res Comm 210:1009-1016.) It is because of the many potential extra-urea cycle, metabolic roles of Arginase II and its up regulation in the hyperargininermic patient, with its implications for gene therapy, that cloning of the Arginase II gene is important. Many different techniques have been utilized to isolate the gene for Arginase II. The presence of six highly conserved regions in the protein, present in the arginases of most species examined, has been critical to the discovery process (Johnson J L, et al., 1984, J Neurochem 43:1123-1126; Ikeda Y, et al., 1987, Arch Biochem Biophys 252:662-674.)